Just finished installing 12mm rods on my Taz 5 X-Axis. I believe they are incorporating 12mm rods on the Taz 6 (although differently than I did it). The reason to increase to 12mm rods is to reduce the sag that occurs (worst at the center of X travel) as the extruder moves in X. The weight of the extruder and carriage causes the stock 10mm rods to deflect too much under the weight. The deflection is significant with respect to the tight tolerances required for nozzle to build bed distance. We typically aim for .1 to .2mm gaps between the bed and the nozzle. The stock 10mm X axis sags more than this amount on my machine. This makes the nozzle either too close to the bed at the center of X travel, or too far away at the extreme ends of X travel.
By doing this upgrade I was able to remove almost all of the sag. My total sag is now less than .1mm through the full range of X travel. This results in a much easier to achieve excellent first layer. It also allows for less trouble when printing wide parts.
The upgrade is a fair amount of work, as you'll have to remove the extruder, carriage, old bearing holders behind the carriage, the x rods and plastic bushings (throw them in the garbage! use linear bearings and hardened steel rods everywhere and thank me later!), the printed stepper mount and idler, and the aluminum mounting plates at each end of the travel. The work is not difficult, but a little time consuming. You'll have to increase the clearance holes in the aluminum mount plates, for each rod, to 13mm (use a 13mm or 1/2" drill bit and small drill press if you have one). But actually the worst part of the job was reclaiming all the heat set inserts from the stock printed parts lol. Anyway this upgrade is Extremely worth it.
You'll need to print one of each of the attached STL's before you begin. Print them with at least 85% infill.
You'll need to order qty 3: LMU12, as well as qty 2: PSFU12-500 shafts From Misumi
Then it's just a matter of replacing all the stock prints with the new ones and replacing the stock 10mm rods and bearings with the stuff from Misumi you ordered. All the other hardware from the stock Taz can be reused. And there is no functional difference between any of the components. No firmware change and no change in how the printer operates, except for greatly improved first layers and easier leveling.
Enjoy! If you have any questions please ask.
ps You'll see Piercet's antiwobble design in the photos too, that is a separate upgrade and I highly recommend that one as well. But it is not required for changing to 12mm. Sorry for any confusion that causes.
pss That mess you see on one side of the double bearing holder (in the picture) was because it was a little loose on the bearings so I added a little goop glue to keep them in place. I was under-extruding when I printed it and didn't feel like printing it again. The STL is correct though.